A weldment includes metal materials that are welded to each other. At least one of the metal materials includes pure copper including an inevitable impurity, more than 2 mass ppm of oxygen, and an additive element selected from the group consisting of Mg, Zr, Nb, Fe, Si, Al, Ca, V, Ni, Mn, Ti and Cr. A method of manufacturing a weldment includes melting a dilute copper alloy material by SCR continuous casting and rolling at a molten copper temperature of not less than 1100° C. and not more than 1320° C. to make a molten metal, forming a cast bar from the molten metal, forming a dilute copper alloy member by hot-rolling the cast bar, and welding the dilute copper alloy member to a metal material. The dilute copper alloy material includes the pure copper, more than 2 mass ppm of oxygen, and the additive element,?